Peasecod-Like Hollow Upconversion Nanocrystals with Excellent Optical Thermometric Performance.

Trivalent lanthanide (Ln)-doped hollow upconversion nanocrystals (UCNCs) usually exhibit unique optical performance that cannot be realized in their solid counterparts, and thus have been receiving tremendous interest from their fundamentals to diverse applications. However, all currently available Ln-doped UCNCs are solid in appearance, the preparation of hollow UCNCs remains nearly untouched hitherto. Herein, a class of UCNCs based on Yb/Er-doped tetralithium zirconium octafluoride (LiZrF:Yb/Er) featuring 2D layered crystal lattice is reported, which makes the fabrication of hollow UCNCs with a peasecod-like shape possible after Ln doping. By employing the first-principle calculations, the unique peasecod-like hollow nanoarchitecture primarily associated with the hetero-valence Yb/Er doping into the 2D layered crystal lattice of LiZrF matrix is revealed. Benefiting from this hollow nanoarchitecture, the resulting LiZrF:Yb/Er UCNCs exhibit an abnormal green upconversion luminescence in terms of the population ratio between two thermally coupled states (H and S) of Er relative to their solid LiZrF:Yb/Er counterparts, thereby allowing to prepare the first family of hollow Ln-doped UCNCs as supersensitive luminescent nanothermometer with almost the widest temperature sensing range (123-800 K). These findings described here unambiguously pave a new way to fabricate hollow Ln-doped UCNCs for numerous applications.